Conduction of water and mineral salts through the xylem vessels is enhanced because the xylem cells are

Step 1: Analyze the question The question asks which feature of xylem cells enhances conduction (the movement) of water and mineral salts. So we need a feature related to flow, not strength or position.

Step 2: The concept Xylem vessels are formed from many dead, hollow cells joined end to end. The cross walls break down, creating continuous, narrow tubes from root to leaf. This structure:

• gives an unbroken pathway for water flow
• supports capillary action and cohesion-adhesion of water molecules in a narrow tube
• reduces resistance to flow because there is no cell content (no cytoplasm or nucleus)

Step 3: Evaluate the options

• A. Thickened with lignin: Lignin gives mechanical strength and prevents the vessels from collapsing under tension. It is for support and waterproofing, not directly for enhancing conduction.
• B. Long, narrow tubes placed end to end: This is the structural adaptation that gives continuous flow and capillarity, so it directly enhances conduction. ✔
• C. Close to the endodermis: Position near the endodermis does not make conduction more efficient.
• D. Centrally placed in the roots: Central placement (as in the root's vascular cylinder) is not what enhances the flow of water.

Step 4: Answer

Exam tip: When a question asks about conduction, think "continuous tube": xylem vessels are hollow, dead, and joined end to end. When it asks about support or strength, think "lignin."